Effect of Insect Damage on the Growth, Yield, and Quality of Sericea Lespedeza Forage

Abstract

Variations in the seasonal abundance of phytophagous foliage-inhabiting insects were examined in sericea lespedeza (Lespedeza cuneata (Dumont) G. Don) during the second growth cycle in 1986 and 1987 and during the first and second growth cycles in 1988. Predominant insect defoliators were grasshoppers and lepidopterous caterpillars, primarily Plathypena scabra (F.) and Helicoverpa zea (Boddie). Predominant sap-feeding taxa were the membracid Spissistilus festinus (Say); plant bugs, primarily Lygus lineolaris (Palisot de Beauvois); aphids, primarily Acyrthosiphon pisum (Harris); and a number of species of cicadellid leafhoppers and pentatomid stink bugs. Grasshoppers, aphids, and plant bugs were most abundant during the first cutting, whereas S. festinus, leafhoppers, and all Lepidoptera were most abundant during the second cutting. Grasshoppers, P. scabra, and total Lepidoptera typically were more abundant in low-tannin than in high-tannin cultivars, but population densities of sap-feeding insects were not associated with the tannin concentrations in sericea lespedeza cultivars. Comparison of insecticide-treated and untreated plots revealed that P. scabra caused extensive defoliation in August and September before the second cutting. No other taxa of herbivorous insects caused significant damage to sericea lespedeza. Defoliation by P. scabra reduced stem height, leaf number per stem, and leaf and stem dry weight but had little effect on forage crude protein and acid detergent fiber content. Yield loss was significant when peak densities of P. scabra were greater-than-or-equal-to 2 larvae per sweep. Peak densities of about four larvae per sweep in 1986 reduced leaf dry weight by 75% and total forage yield by about 40%. However, substantial yield losses were avoided by harvesting early.